Don't skip parent/previous sibling updates on --web uploads

We have recently implemented SHA-256 skips when article content hasn't changed.

But we also need to check if the parent or previous sibling has changed, and if it has then update that.

We could just return parent and previous sibling on the /hash endpoint.

Or we need to add that information to the SHA.

Ideally we should also have a way to change the tree without re-render, though we could start with re-render for simplicity.

This actually breaks uploads because it leads to inconsistencies when finding previousSiblingId.